Automatic band-width regulation means



June 17, 1941. H. SPREINE AUTOMATIC BAND-WIDTH REGULATION MEANS FiledJune 13, 1939 A vc Jam/ML INVENTOR HEINRICH SPR E/NE BY #5! I ATTORNEYPatented June 17, 1941 FFICE AUTOMATIC BAND-WIDTH REGEEATION MEANSHeinrich Spreine, Berlin, Germany, assignor to Telefunken Gesellschaftfiir Drahtlose Telegraphic in. b. 11., Berlin, Germany, a corporation ofGermany Application June 13, 1939, Serial No. 278,838 In Germany June16, 1938 Claims. ((31. 250-) Arrangements are known in the earlier artfor providing an automatic band-Width variation in receiving apparatusin which the band-width is automatically varied as a function of thesignal strength in such a way that the band-width is made small when theincoming or signal intensity is reduced, while it is made large when thesignal strength is large.-

Arrangements of this kind are rather complicated and expensive when theband-width is varied not merely in a single circuit, but in severalcircuits simultaneously, and also if this variation is accomplished notby a variation of the damping, but change in coupling. According toprior practice, variation in the coupling has been efiected mostly by amechanical adjustment of coupler coils. However, such ire-adjustment ofthe coupling requires considerable mechanical power; indeed, this powerwhere automatic regulation is to be effected by tube circuits would beobtainable only by the use of tubes of large power.

According to the present invention, the means designed to produceband-width variation, which a mechanical restoring or retractile forcetends to force constantly in the direction of minimum band-width, iscoupled by mechanical means with the tuning shaft of the receivingapparatus in such a way that when the tuning shaft is turned theband-width is enlarged. But the said coupler or loclnng means isoperative only above a certain threshold value of the signal strength.

The advantage underlying the invention is that the power required for amechanical adjustment of the band-width is furnished by the user of theset. In fact, the signal oscillation is merely called upon to render thecoupling means operative, and this requires a substantially lesserexpenditure of power. The band-width variation means, therefore, may bebuilt the same way as has heretofore been customary, that is, forinstance, with mechanically adjustable coupler coils. If the amplitudeof the signal oscillation is equal to zero or very small, then thebandwidth varying device by action of the retractile force is soadjusted that the band-width assumes a minimum value. However, as soonas in the course of the tuning of the set the latter is roughly tuned toa certain station, then the coupling device becomes operative, and thebandwidth regulator is driven by the tuning means which must be turnedanother distance for exact and sharp tuning, with the result that thebandwidth is enlarged. The band-width which will be finally adjusted inthe receiver will be so much larger, the stronger the signal of theincoming transmitter station since in the case of a powerful transmittera certain threshold value will be attained by the signal intensity evenwhen the set is still a greater distance away from sharp tuning than inthe case of a station whose signal comes in feeble. This situation willapply to all receivers with a normal selectivity curve in which theautomatic volume control does not equalize completely.

An exemplified embodiment of the invention is illustrated in theappended drawing in which the single figure discloses so much of a radioreceiver as is necessary for a proper understanding of the invention.The coils L1 and L1' wrapped on a form or support shall be assumed toform the two coils of a tuned I. F. band-pass filter of the receivingapparatus. Coil L1 is in coupling. relation with the coil L1 by means ofthe coupling coil K1 comprising only a few turns and being connected inseries with it. In the position shown in the figure, the coupling isvery weak since the axes of the coils L1 and K1 are at right angles toeach other. If, then, coil K1 which is revoluble about the shaft M1 ismoved out of its normal position towards any side at all, the couplingat all events becomes stronger and the band-width is thus enlarged.

The coils L2, L2 shall be assumed to constitute, in a similar way, asecond I. F. band-pass filter; they shall be coupled with each other bythe coupler coil K2 which is turna-ble about the axis M2.

The turning of the coupling coils is effected by the lever arms A1 andAs the lower ends of which are secured to a metal band B. The latter atboth ends is connected by way of tractile springs F1 and F2 with thestationary casing of the receiver and it is passed over rollers R1 andR2 and a drum T. The latter consists of a semiconductive material suchas agate or marble, for instance. The shaft W thereof is in mechanicallycoupled relation, on the one hand, with the shaft of the tuningcondenser C, and, on the other hand, with the tuning knob K. The drum,for instance may be secured directly on the shaft of the tuning knob Kwhich is coupled with the rotary condensers by a chord or cable.

The springs F1 and F2 are of such dimensions that normally the couplercoils K1 and K2 will occupy the position as shown. The ribbon or band Bis placed on the smooth drum T so loosely that even when the tuning knobK is rotated rather rapidly the normal position (or rest) is practicallyunchanged.

In sliding contact with the drum is a metallic brush S by way of whichthe drum is fed with the D. C. voltage obtained by rectification of theI. F. oscillation and which serves at the same time for automatic volumecontrol. As soon as the drum in reference to the grounded band B has apotential which surpasses a certain minimum level, strong forces ofattraction will be set up between the band and the surface of the drumby virtue of the well-known Johnson- Rahbek effect as a result of theincreased adhesion between the two boundary layers, and this sets upappreciable friction. The result is that the band is driven by the drumand thus by the tuning knob, and the coupling coils K1 and K2 are turnedwith the consequence that the coupling and the band-width of thereceiving apparatus are increased.

The amount of increase of the band-width when tuning to a station is afunction of the angular range covered by the tuning shaft figured fromthe position in which the abovethe drive.

The control potential may be amplified by a D. C. amplifier. t isalsopossible to cause the rectified signal oscillation to actuate arelay above the threshold value, the relay causing a potential which ishigh with respect to ground to be impressed upon the drum.

Under certain circumstances also the I. F. potential itself may beapplied to the drum or the band.

where the tuning is eifected not manually, but by motor drive, and wherethe adjustment to a definite station is caused by the actuation of acoordinated press button. If for this purpose the tuning means are sodesigned that the adjustment occurs only in one direction, then thebandwidth variator as usual may be so designed that from the position ofminimum band-width it can be changed in only one direction.

What I claim is:

1. In a receiving system, a band-pass network provided with means forvarying its signal response characteristic, means for tuning thereceiver to a selected station, and means under the direct control ofthe tuning means and movable in response to the strength of the receivedsignal for automatically adjusting the signal response varying means.

2. In a receiving system, a band-pass network,

means for varying the signal response charac-' teristic of said networkfrom a condition of sharp selectivity to one of high fidelity, means fortuning the receiver to a selected station, and means under the directcontrol of the tuning means and movable in response to the strength ofthe received signal for automatically adjusting the signal responsevarying means, said response varying means normally providing a sharpselectivity adjustment up to a predetermined value of signal strength,and for increased signal strength be- The invention will be found usefulalso in cases yond said value providing varying degrees of high fidelityadjustments. I

3. In a receiving system, a band-pass network provided with means forvarying the width of the band transmitted thereby, means including acontrol shaft for tuning the receiver to a selected station, and meansunder the control of the tuning means and responsive to the strength ofthe received signal for automatically adjusting the band width varyingmeans, said adjusting means comprising a member connected to the bandwidth varying means and adapted to be selectively operable by the tuningcontrol shaft, said member normally maintaining said varying meansinnarrow width adjustment, and means for establishing between saidmember and the control shaft a potential difference proportional to thesignal strength, a minimum potential difierence being required to causethe control shaft to operate the member, the arrangement being such thatduring the process of tuning, for received signals, below the minimumvalue the member is inoperative and the adjustment of the network issuch as to pass a narrow band, whereas for received signals above saidvalue the control shaft operates to move said member and consequentlythe band width varying means for adjusting the network to pass a wideband.

4. In a receiving system, a band-pass network provided with means forvarying the width of the band transmitted thereby, means including acontrol shaft for tuning the receiver to a selected station, and meansunder the control of the tuning means and responsive to the strength ofthe received signal for automatically adjust ing the band width varyingmeans, said adjusting means comprising a member contacting with thetuning control shaft and connected to the band width varying means, saidmember nor mally maintaining said varying means in narrow widthadjustment, and means for establishing between said member and thecontrol shaft a potential difference proportional to the signalstrength, a minimum potential difference being required to cause thecontrol shaft to frictionally engage and drive the member, thearrangement being such that during the process of tuning, for receivedsignals below the minimum Value the frictional coupling between shaftand member is insufficient to move the latter and the adjustment of thenetwork is such as to pass a narrow band, whereas for received signalsabove said value the frictional coupling is sufficient to move saidmember and consequently the band width varying means for adjusting thenetwork to pass a wide band.

5. In a receiving system, a band-pass network provided with means forvarying the width of the band transmitted thereby, means including acontrol shaft for tuning the receiver to a selecte station, and meansunder the control of the tuning means and responsive to the strength ofthe received signal for automatically adjusting the band width varyingmeans, said adjusting means comprising a semi-conductive sleeve mountedon the control shaft, a metal strip adapted to rest on said sleeve andhaving a connection to the band width varying means, spring means fornormally urging said varying means to the narrow width adjustment, andabrush contact rid ing on the semi-conductive sleeve and having apotential proportional to the signal strength impressed thereon wherebythere is established between said band and sleeve a potential differenceproportional to the signal strength, a minimum such as to pass a narrowband, Whereas for received signals above said value the frictionalcoupling is sufficient to move said band and. consequently the bandwidth varying means for adjusting the network to pass a wide band.

HEINRICH SPREINE.

